Field of the Invention
The present invention relates to an air conditioner for a vehicle.
Description of Related Art
In electric vehicles, because the engine cooling water cannot be used to heat the vehicle interior, an air conditioner for a vehicle that utilizes a heat pump cycle is employed.
In this air conditioner for a vehicle, because the heat exchange medium absorbs heat during a warming operation in the external heat exchanger, if the outside air temperature is extremely low, then in some cases, frost formation may occur on the surface of the external heat exchanger. If frost formation does occur, then because the heat transfer rate deteriorates so that the heat absorption is inadequate, a problem arises in that the warming effect inside the vehicle compartment is insufficient.
Therefore, a heat-pump-type air conditioner is known that determines a frosting state based on the temperature difference between the outside air temperature detected by an outside air temperature sensor and the temperature of an external heat exchanger detected by a temperature sensor for the external heat exchanger so as to start the control for defrosting (for example, refer to Japanese Unexamined Patent Application Publication No. 2000-283611).